Data-reducing coding method for transmitting information from a transmitter to a receiver

ABSTRACT

A coding of images and originals, for example, for telefax and color television, allows transmission time to be shortened, in particular in the case of black and white digital or numeric longitudinal coding. For that purpose, the same code words for black and white are provided also for different numbers or digits. As discriminating criterion, the input sequence of black and white is used. During coding of several successive white lines, transmission time can be further shortened in that the coded number of white lines is provided before or after the code word for the white line. During gray coding, transmission time is in particular reduced by subdividing the gray scales or binary code words, if necessary with deliberate redundancy, since in this case many characters occur successively and are then transmitted in the same way as the white lines. During color image transmission, transmission time is further reduced by code multiplexing and if necessary by QAM-based transmission, whereas in addition the PAM-coded information is D.C. biased. The sum alternating current thus varies in phases in the range of 90 degrees only.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of application Ser. No. 08/108,594, filedon Sep. 3, 1993, which is the U.S. National Phase Application ofPCT/EP92/02977, filed on Dec. 23, 1992.

TECHNICAL FIELD

The present invention is concerned with the coding and transmission ofimages and patterns, in particular for telefax and for television,especially color television.

STATE OF THE ART

Facsimile equipment is split into standard groups in accordance with thetransmission time. Groups 1 and 2 with point by point scanning havealready been superseded by Group 3 equipment. The latter represents adigital transmission system in which the picture scanning points ofequal brightness are brought together in an unbroken sequence andcombined into a code word. Such methods are known as one-dimensional.The MHC method is such a one. The two-dimensional process is built up onthe same principle. In this first a reference line is scanned and in thesubsequent lines only any departure from the reference line is coded.The MRC method operates in accordance with this principle. Then there isthe MMR code, in which after a coded reference line a large number ofsubsequent lines are coded two-dimensionally. In the run-length coding,for each number of picture points per line, a special binary code isdetermined for white and black, eg. 1 white=000111, 1 black=010, 2white=0111, 2 black=11, . . . 20 white=0001000, 20 black=00001101000.Such coding goes up to picture point number 63. Then one starts againfrom the beginning with an additional section code word for white andblack. For transmitting these coded numbers in particular, thephase-difference or amplitude-phase-difference modulation is employed.

In gray-scale scanning the gray values were divided into gray steps andconverted in more or less close patterns of black and white dots. Inthis way, as is known from the Dither printing process, a correspondinggray step is taken in by the eye. In the coding of color images andpatterns expensive processes have hitherto been necessary. To someextent similar to the coding in the NTSC, PAL and SECAM systems.

DESCRIPTION OF THE INVENTION

A drawback of these known methods is in facsimile the relatively longtime taken up for transmission and the large outlay for coding and thenecessary large bandwidth, in particular in the coding and transmissionof color images. As hitherto several carriers were required in colortransmission, distortion by mutual interference, such as for examplecross color, cross luminance, have arisen.

The aim of the invention is to provide such a coding that theinformation can be transmitted in a shorter time period than hitherto,but with at least the same transmission security. This is attained inthat the run length coding in numbers or digits for black and whitetakes place by means of the same code words for different numbers ordigits. This is possible because the pick-up sequence black/white isused as a criterion. A further shortening of the time during the codingof white lines is therefore possible in that the respective coded numberof the white lines is disposed ahead of or behind the marker for "whiteline". During color transmission a savings in time and effort isachieved by means of multiplex-code coding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall representation of a facsimile equipment.

FIG. 2 shows an alternating current code in which the characteristicstates are marked by the amplitudes of the half-waves. Multi-valuecoding is achieved by 2 alternating currents, displaced in phase by 90degrees, and added together for transmission.

FIG. 3 shows a multi-value alternating current code in which severaladded alternating currents are provided, of which the frequency alwayslies half the frequency higher than the primary alternating current.

FIG. 4 shows an alternating current code in which the coding isdetermined by the duration of the cycles and the amplitudes of thehalf-waves.

FIG. 5 shows an overall view of phase shifts by cycle durations.

FIG. 6 shows a circuit for producing cycle durations and amplitudestages.

FIG. 7 is a diagram of the addition of phase stages.

FIG. 8 is a vector diagram for illustrating jumps in phase on alterationof an amplitude in 90 degree-phase-shifted alternating currents, byaddition of them.

FIG. 9 shows the generation of amplitude stages.

FIG. 10 is an illustration of the binary code elements for 6 lines forcode-multiplex coding.

FIGS. 11 and 12 are illustrations of operating characteristics in thecombination of several lines.

FIG. 13 shows a quaternary code.

FIG. 14 shows a color television receiver for code-multiplex reception.

FIG. 15 shows oscillation curves for the color-difference signals withand without equal current bias with PAM and step signals.

FIGS. 16, 17, 18, 19, 22 coding of color-TV signals.

FIGS. 20, 21 a narrow-band information channel between TV channels.

FIGS. 23, 24, 25 a rearrangement of code words.

FIGS. 27, 28, 33 coding and decoding of unchanging running lengths.

FIGS. 29, 30, 31, 32 coding of gray tones.

METHOD OF PUTTING THE INVENTION INTO PRACTICE

In FIG. 1 as shown a general view of a facsimile equipment. The readingunit L has the function of converting the pattern which is to betransmitted into analogue electrical signals. They are then convertedinto digital signals in the color Cod. The modem Mo is provided fortransmission. The port unit AS serves to match to the telephone network.The incoming signals reach the decoder Decod through the port AS and areconverted back to the original form in this unit. Writing onto the paperthen takes place in the printer unit Az. A central control ZSt controlsthe telecopier system and coordinates the facsimile transmission.Control is through the operating field B.

The invention is concerned with the coding and transmission of thepicture points or pixels. According to the invention a run-length codingoperates in the manner in which the respective number of the white orblack picture points is coded in digits or symbols. For example if 28white pixels are scanned successively, there takes place a coding of 2white followed by 8 white. If 6 black pixels are then scanned, thesymbol 6 black is coded. A code is therefore required for the symbols 0to 9 white and for the digits 0 to 9 black. Twenty combinations arenecessary for these symbols. On the same basis naturally also theparticular characteristic symbols, such as the start and stopindications (EOL) or the EOP, MCF or other criteria could be coded. Forcoding these 20 symbols and the criteria necessary for operation a quitesimple binary or multi-value coding can be provided. In order to obtain20 combinations 5 bits are necessary in accordance with the teleprinteralphabet No. 2. With this one can therefore code 32 combinations andcriteria. Since at the most 4-digit numbers are present, if for example1728 pixels are present per line, one can with the remainingcombinations also code 2-digit numbers in the manner in which onecombines the thousands which are present with the related hundreds toform a code, eg. the numbers 10, 11, 12, . . . 17. For the coding of atthe most 1728 pixels one then arrives at 3 codings. A distinctionbetween white and black is not necessary in this case because thesubsequent number codings reveal whether the 2-digit number belongs towhite or black. If for example 1728 white pixels are coded first thenumber 17 and then the number 2 white and 8 white are coded. By the 2and 8 white it is revealed that the 17 belongs to white. According tothe prevailing standard every line begins with a white sequence. Thisstandard remains unaffected by the invention. The invention can also beemployed using the MRC or MMR code or a similar code both in thereference lines and also in the subsequent lines with the departuresfrom the reference lines, in which the number or the difference numberof the pixels can likewise be coded as digits or symbols. Since in thesequence or run-length method alternate numbers are always present forwhite and black, one can also, for economy in combinations, first codeall white numbers and subsequently, in accordance with a criterion code,all black numbers with the same code. However then every run-lengthnumber must then be associated with the same number of points. One pixelmust then be coded with 001, 12 pixels with 012. In black one wouldalready emerge with 2 points. For the 3 and 4 digit exceptions a uniqueadditional criterion would then have to be provided. For thetransmission itself, as also hitherto, the phase-difference ofamplitude-phase-difference modulation can be employed. Further codingsare explained in the following. In FIG. 2 there is illustrated aduo-binary half-wave code. The amplitudes of half-waves (if freedom froma DC component is necessary one will provide cycles for these) of twoalternating currents of the same frequency with a 90 degree phasedisplacement serve as coding elements. The two are added fortransmission so that in the transmission only one alternating current ispresent. The characterizing conditions in the example are (0)=aP11,(1)=aP1, aP2, . . . (2)=aP3, . . . . Using this principle the bit numbercan be substantially increased if for example one provides anarrangement in accordance with FIG. 3. Therefore one or more codingalternating currents are provided of which the frequency or frequenciesincrease respectively by half the original frequency, eg. with a basefrequency of 1000 Hz, to 1500 Hz. Again for the coding 2 codingalternating currents are provided of 1500 Hz, displaced in phase through90 degrees. With 2 added coded alternating currents one would achieve 10bits with one cycle or one and a half cycles. One can also provide anamplitude/phase code. Such a code is illustrated in FIG. 4. The phase isassociated by the half-wave period duration and to the amplitudes ofthese half-waves are associated two characteristic conditions. With 2phase characteristics and 2 amplitude characteristics one obtains with 2points 4 to the power of 2 and with 4 points already 4 to the power of 4combinations. For achieving freedom from a DC component, the positiveand negative half wave is necessary for a characteristic. The number ofphase characteristics is also a problem in the transmission technologyfield, and the running time must be taken into account. In FIG. 5, 5phase characteristics are provided. The normal phase is f=360 units. Ifthere is a change to 405 units and the phase displacement remains, thenin the next half cycle or cycle again a conversion must be made to ahalf cycle or cycle duration of 360 units. A circuit by which suchphase/amplitude coding could be achieved is illustrated in FIG. 6. Thecounter unit Z is controlled by pulses of a predetermined frequencygenerated in the oscillator Osc. The duration of the half cycles orcycles of the rectangular pulses to be generated is then determined bythe outputs Z1, Z2, . . . . The control of which cycle duration or whichoutput is to be in action is achieved by the coder Cod. If the halfcycle or cycle duration of the output Z1 is to be in action, the gate G3is opened through g3. If the output z1 is reached, the gate G3 is inaction and thereby controls the electronic relay ER. The start of therectangular pulse is characterized through A. The amplitude of therectangular pulse is determined by the voltage applied to ER through (A)(++), (+), (-), (--). Then at the output of ER there are obtainedrectangular pulses of predetermined duration and amplitude. If onewishes to have sine-like half-waves for transmission, the rectangularpulses are conducted to the lead through a low-pass filter TP, thetransformer U and if necessary though a filter Fi.

Where only narrow bands at high frequencies are available it is ofadvantage to undertake the amplitude and/or phase changes of thecharacteristics in steps so that one only obtains very narrow frequencybands. For example, as illustrated in FIG. 7, if the normal phase orduration is 360 units and if this is shortened four times by 10 units,then with the 4th shortening there is a difference of 40 units ascompared with 4×360 units. From f=1/T one then obtains the phase stepfrequency if one associates a predetermined time with the 360 units. Ifafter the 4 abbreviated periods one changes back again to the normalperiod duration of 360 units then a running phase displacement of 40units remains. This is more closely explained in European PatentApplication number 0329158. On this basis one can undertake anadvantageous coding in that for example 3 phase shifts (normal phase,phase advance and phase delay) and 3 different duration values areenvisaged. Then simultaneously the phase jump steps are contained withinthe periods. If one takes 100, 150 and 200 as the duration figures and a45 degree advance and 45 degree delay as the phase displacement, one has9 coding steps. With 2 points one already has 9 to the power of 2combinations and with 3 points 729 combinations. In this regard thereare different variations in relation to number and phase. The alterationof a characteristic condition is indicated in the example by a change inamplitude. The amplitude can naturally also be provided in steps. With aphase jump of 45 degrees there results, in a 100 periods a phase changeof 0.45 degrees for each period. As in a burst in television, in thereceiving a reference phase is also necessary and here it can forexample be the normal phase. With a channel band width of 64 KHz asmaller period number can be provided. The alteration of frequency isadvantageously undertaken on passage through zero, also tolerances couldboth be permitted in the period number and also in the phase.

Where the amplitudes of two coded alternating currents with a phasedisplacement of 90 degrees are provided as the characteristics, one canalso here undertake each change in characteristic by a number ofamplitude steps. It is known that in the addition of such alternatingcurrents in amplitude jumps, phase jumps also arise. In FIG. 2 suchcoded alternating currents ate illustrated with duo-binary coding. InFIG. 8 there is illustrated a vector diagram of such coded alternatingcurrents with binary coding. The characteristics are Uk+U and Uk, Vk+Vand Vk. On alteration of the amplitude, phase jumps of q can arise. Inorder to avoid these, the changes in amplitude are carried out in steps,illustrated in the figure at Stu and Stv. FIG. 9 illustrates a circuitfor generating such steps. In the example the alteration is achieved bymeans of resistors R1, R2, . . . which are introduced into thealternating current circuit by means of an electronic replay eS. Thecontrol takes place in this arrangement during the passage through zeroin that by means of a limiter B synchronizing pulses are generated, bywhich the coder, which switches the electronic relay, is controlled.

For transmission one can also combine several lines together andtransmit them in code multiplex. One could then also distribute the EOLand other marks on the combined lines. The code-multiplex combinationcan for example take place in that the symbols of the individual linesare binary-coded, synchronized and combined in parallel and combinedwith a multi-value code word. Six lines are combined together inaccordance with this method in FIG. 10. The code word S1 is then made upof the binary code elements 100100, S2 of 001000, S3 of 100011, and soon. The start and stop and also if necessary other codes can be spreadover all the lines. Examples of this are illustrated in FIGS. 11 and 12.These characteristic marks can be identified by one or several parallelcode words. In FIG. 11 there are 4×6 binary code elements. In FIG. 12 4lines are combined together, 4×4 code elements being provided for thestart and stop marks. One can also assign a special code to the lastline. A further reduction of the transmission time can be achieved inthat lines of the same code length or similar code length can becombined by code-multiplexing with the interposition of a store, a linemark being necessary for each line. With DIN A4 documents there are eg.1100 lines. Therefore 1100 combinations must be provided for the linecoding. These could however at the same time also be used as the EOLmarks. The code-multiplex combination of the symbols of numbers isachieved advantageously with a high-value, eg. quaternary or octonarycoding. In FIG. 13 there is illustrated an example of a quaternarycoding. Eight bits are necessary for coding 256 combinations, and thesecan be represented using eight binary code elements. One can also bringtogether the eight code elements into 4 dibits, so that only 4 codeelements are necessary for coding the 8 bits. In the example of a symbolcoding for 10 white, 10 black, for the thousands and other symbols 32combinations, that is to say 5 bits, are necessary. With quaternarycoding one will always combine 2 symbols in series or parallel, so thatdibits can always be formed. With a 4-stage coding one then obtains,with 5 positions, 4 to the power of 5, that is to say 1024 combinations,and therefore 10 bits. If binary half-wave code elements are provided inFIG. 2, 5 half-waves are necessary respectively with the 2 codedalternating currents. All the lines having only white can have their ownshort code. One can also insert in advance the code word for the whitelines and in the subsequent part then only raise the line numbers of thewhite lines and give a special mark again at the end of the white lines.This method of transmitting the white lines can be employed in all knowncoding and transmission methods. Of course white lines do not need to beprinted so that one only needs to provide one further circuit at thereceiver. Such electronic circuits are known from circuits of electronictypewriters and need not be further discussed.

In the transmission of documents and images it is sometimes alsonecessary to code and transmit gray values. In one known code in thisfield the different gray steps are illustrated solely by white and blackpixels. In such an arrangement resource is had to the Dither methodalready known in printing technology. In this the gray steps areconverted into more or less dense patterns of white and black pixels.The scanning unit evaluates correspondingly the analogue voltage valueswhich are received from the reflecting surface are the gray steps, eg.16, and stores them. A white surface corresponds to the gray value 0 anda black surface to the gray value 16. Coding and transmission can againbe achieved on the principle of run length, one can also code the steps,eg. 1, 2, . . . 16 and transmit them or also the respective analoguevalue.

To reduce the transmission time 2 or 3 gray steps can be combined toform a code word. The respective gray value can also be transmitted inanalogue form, in that the voltage values or pulses which indeedcorrespond to PAM pulses can be converted into pulse lengths and withthe aid of an electronic relay into rectangular pulses. The length ofthe respective rectangular pulse then corresponds to the height of theobserved voltage value. One can then produce a coded alternating currentthrough a filter. The half cycle duration or cycle duration of the halfwaves then contains the information. This principle is already disclosedin European Patent Application Publication Number 0 329 158.

For the coding and transmission of colored images and documents, eg. forfacsimile and color television, expensive methods have hitherto beenemployed. In facsimile (telefax) it is advantageous to transmit thecolor components of the primary colors because in many cases the paperat the receiver comprises 3 super imposed photo layers. Color televisioncoding methods are known from the NTSC-PAL-and SECAM systems and from myU.S. Pat. No. 4,675,721 and German Patent Applications P3 223 312, P3226 382 and P3 709 451. In the present method the transmission of allthe color information signals takes place using only one carrier orhowever the carrier is provided directly for information coding.

Where one codes and transmits only the color components, gray values areto be transmitted for the green, red and blue. In facsimile in such anarrangement a smaller number of steps (with digital coding) than intelevision is sufficient. For example, with 16 gray values for eachcolor one can therefore combine respectively the 3 values of the primarycolors by code-multiplexing. For this 12 bits are necessary and they canbe coded with the code already used, such as for example with thehalf-wave code of FIG. 2 or with a phase code in combination with aperiod number of amplitude steps. Also the narrow band coding can beprovided if for example one considers phase steps and/or amplitude stepsand/or steps in the number of, for example, periods.

One can naturally also use these codings when one transmits the colordifference signals and the luminance signal, if necessary alsocode-multiplex. Where the code-multiplexed information is to betransmitted by radio, eg. for television purposes, where the highfrequency transmitter is simply modulated with the coded alternatingcurrent. The receiver is then constructed like a supernet radio receiverand one such is illustrated in FIG. 14. Only a further decoder DC isnecessary after the demodulator DM. More is revealed by European PatentApplication Publication Number 0 329 158.

In the television systems used up to now for example the color signalsR-Y and B-Y are respectively modulated onto a respective carrier of thesame frequency with a phase displacement of 90 degrees. According to thepolarity of the respective color voltage the carrier has madecorresponding jumps in phase. Both carriers are added together fortransmission. The sum vector which represents saturation of the colorsdetermines the color by its angle in the color circle. In FIG. 15analogue signals are shown by R-Y and B-Y and FIG. 16 shows acorresponding vector diagram. A drawback of such transmission is thatthe small values are adversely affected by distortion. By means of a DCbias voltage, indicated in dotted lines in FIG. 15, one can make thevoltage values solely positive, so as to produce a vector diagram asillustrated in FIG. 17 on addition of the carriers. As in PAM it is ofadvantage to scan the color signals and construct them as staircasesignals. If the luminance signal is scanned likewise in synchronism withthe color signals, the color signals being scanned alternately andalternating current carriers which are mutually displaced by 90 degreesmodulated onto the signal, then on an addition of the carriers with analternating current one can transmit the whole FBAS signal, then on anaddition of the carriers with an alternating current one can transmitthe whole FBAS signal. In FIG. 18 is illustrated the step-shaped PAMsignal and in FIG. 19 a corresponding vector diagram. With DC bias onall PAM pulses then with vector changes a phase jump of 90 degrees cannever arise as also follows from FIG. 8. Using intermediate storage onecan mix the pulses so that one color pulse comes on 3 or 4 luminancepulses. With this kind of coding the information is representing by themagnitudes of the sum vectors and by their phase position. If a narrowfrequency band is necessary for transmission, one can consider using themethod of FIG. 8.

Telefax can also be introduced into television for particularprofessional groups, eg. for lawyers in order to receive new parts ofbasic law, for tax advisers, for doctors and so on. This could forexample be achieved in the way that one uses the second sound channelfor this purpose. The LF output of this channel must be connected tosockets so that at any time the telefax apparatus could be connected toit. Such a connection could also be made available only on payment of afee. The sound carrier could simultaneously be coded in a narrow-bandform as an information carrier. Naturally one could also use the otherknown frequency and time multiplex methods for the second channel fortelefax. Using the sound carrier so much can be coded that one can stillcode other information as well as the second sound channel. For exampleif 100 periods are provided per code element, then with a sound carrierof 5742 MHz one can make 57420 code elements. One can also introduce anadditional channel between the television channels, in that betweensound channel 2 and the following television channel one provides acarrier which is employed simultaneously for narrow band phases and/oramplitudes and/or different numbers of periods. By a correspondingseries resonance circuit one can, as shown in FIG. 20, make availablethe band width for such a carrier. In the drawings the series resonancecurve is indicated at RR and the carrier at BTZ. IN FIG. 21 isillustrated the principle of the arrangement of a narrow-band channelbetween 2 television channels. The carrier frequency would be around195.25 MHz. Small frequency variations are always available by thestep-wise changes in phase and amplitude. This principle is already moreclosely described in German Published Specification 4025026.

In FIG. 22 there is illustrated a method in which the analogue ordigital information can be transmitted on two channels with only onealternating current. In the example it is the luminance signal Y and thecolor difference signals R-Y and B-Y. The Y signal and the two colorinformation signals are alternately pulse-amplitude modulated and formedinto step signals, which is certainly already known. This is illustratedin FIGS. 22a and 22b. Both the signal sequences are modulated onto arespective carrier alternating current of the same frequency, whichhowever are phase-displaced through 90 degrees. The carrier frequency inthe example of FIG. 22d is advantageously synchronized with the pick-offfrequency and is an integral multiple of the pick-off frequency. The twocarrier alternating currents FIGS. 22c and 22d, are added in sequence.This results in a sum alternating frequency Su of FIG. 22a of the samefrequency as the two carriers. On the modulation of the step signalsonto the respective carrier alternating currents and also in theaddition of the two carriers jumps in phase arise. These jumps in phaseof the sum alternating current contain in conjunction with therespective amplitudes the information of the step signals of FIGS. 22aand 22b. This sum alternating current can naturally be transmitted inthis form to the receiver. In the evaluation of the phase position areference current like the burst is necessary. Such evaluation is forexample known from the PAL system.

With the customary methods, during color image transmission the 3 ordersof the base color separations for green, red and blue or the luminancesignal Y and the color type signals, such as the color differencesignals R-Y and B-Y are transmitted, for example. In many cases,quadrature amplification modulation is provided for the transmission.This can take place by means of direct transmission of the codedsignals, in that the amplitudes of half-waves or periods are used, whichare distributed on two alternating currents of the same frequency,phase-shifted by 90°. For transmission, the two alternating currents areadded together. In case of indirect transmission, for example, thePAM-modulated signals are coded by means of the amplitudes ofrectangular pulses, staircase signals, or by the amplitudes ofhalf-waves or periods of alternating currents and are respectively linedup into two uninterrupted sequences and modulated onto two alternatingcarrier currents, phase-shifted by 90°. These are then added togetherfor transmission. Since 3 values must always be transmitted during colorimage coding, such as the base color separations for green, red and blueor the luminance signal Y and the color type signals, such as the colordifference signals R-Y and B-Y, a cyclic interchange is required, takinginto consideration the weights, which looks like this, for example: basecolor separations gr/rt, rt/bl, bl/gr, gr/rt, . . . luminance signal andcolor difference signals Y/R-Y, Y/B-Y, Y/R-Y, . . . . In this case, withthe base color separations an equal weight is used, and with theluminance signal and the color difference signals a weight of 2.1.

The coding or sum alternating currents can simultaneously be provided astransmission alternating currents. If direct current biases are providedwith the PAM pick-ups, they are made of such strength that the usefulsignals lie above the noise or interference level.

Based on the requirements, it is possible to use the same code words forwhite ws and black sw for the run lengths. Each line must always startwith a white run length. If the line starts with the color black, thewhite run length zero is transmitted first. In addition, the code wordEOL is transmitted at the start of each page and the end of each line.With this, the synchronization of the white/black sequence is alsofixed, which is of particular importance during evaluation. Thefrequency of the appearance of lengths was taken into account duringnumber coding. If it is intended to transmit written material, short runlengths, such as 2, 3, 4 often appear with black. Correspondingly smallcode words, such as 11, 10, 011 were assigned to these. As aconsequence, frequency will be taken into consideration when using thesame code words for white and black. In accordance with the presenttable, the numbers 2 to 7 occur with the same frequency with white,while with black 2 and 3 occur most frequently. Thus, in accordance withthe invention, with black the shortest code words are used for thenumbers 2 and 3, these are used with white for the number 4 and 5, forexample. Half of the codings are then no longer required. Coding of thelarger numbers will no longer be provided with black, because they havetwelve digits, while they have only eight digits with white. In case ofa greater horizontal resolution, a corresponding frequency adaptationwill of course be made. If a change from eight to sixteen pixels permillimeter is made, 2sw is increased to 4sw pixels, i.e. the number 4than occurs most frequently with black. The coding possibilities forsome of the most frequently occurring numbers are shown below.

    ______________________________________                                                         Horizontal Resolution, for                                                    example 16                                                   wsL  wsC      swL     swC    wsL   wsC  swL   swC                             ______________________________________                                        0    00110101                                                                 1    000111   0       00110101                                                2    010      1       010     5    010   3    010                             3    11       2       11      6    11    4    11                              4    10       3       10      7    10    5    10                              5    011      4       011     8    011   6    011                             6    0011     5       0011    9    0011  7    0011                            7    0010     6       0010   10    0010  8    0010                            8    0111     7       0111   11    0111  9    0111                            9    1000     8       1000   12    1000 10    1000                            ______________________________________                                    

On the transmitting and receiving end it is only necessary to wire thecoding and evaluation device appropriately for obtaining the desiredcodings or run lengths. Some circuits for the assignment of the codewords to the predetermined run lengths are shown in FIGS. 23, 24 and 25.A white run length or a zero always follows after the evaluation of theEOL mark. By means of a circuit, which is known, the sequencewhite/black is switched on after the evaluation of the EOL mark and acorresponding potential, for example high h, is applied to ws/sw. If inFIG. 3 the number 1 was evaluated and the sequence happens to be whitews, lw h/h is present at the gate, so that it becomes active and marksthe number white ws1. If the number 5 was evaluated and the sequencehappens to be black sw, the gate 5s is twice hh, so that the number ismarked black sw5.

A circuit for the assignment of the evaluated code words for differentnumbers for white and black in accordance with the left side of thetable is shown in FIG. 24. In this case the code words sw 1 to 6 arealso provided for the numbers 2 to 7. If, for example, the code word is1sw and the sequence is marked white ws, the gate G1 becomes active andthe number 2 white is marked 2w. If the code word 5sw is evaluated andthe sequence is marked white ws, the gate 10 becomes active and thenumber is marked black 5s. If the code word white 2ws is marked and thesequence is marked black sw, the gate 14 becomes active and the number 7is marked black 7s.

An example is shown in FIG. 25, wherein switching to various run lengthnumbers as a function of the respective resolution of 8 or 16 pixels permillimeter takes place. It is of course possible that such switchingtakes place by means of an individual chip. In the table, examples areshown for the assignment for 8 pixels to the left and 16 mm to theright. If, for example, the resolution is 8, a potential h is applied to8 in the receiver. If in this case the code word 3sw is evaluated, thegate G4 becomes active and applies such a potential to G3 and G4, thatwith a white marking ws G3 becomes active and with a black sequencemarking G4 becomes active and marks the numbers white ws4 or black sw3.If subsequently after G1 another potential is required, it is possibleto switch a potential reversing gate downstream of G1, for example aNOT-gate. If the resolution 16 is marked, G2 becomes active andsubsequently, as a function of ws or sw, the gate G5 or G6. Thus, thenumber ws7 or sw5 (see the Table) is marked.

In actual use, the new coding in connection with group 3 will be appliedin the transition state by providing a switch-over to the new coding.The code words not used would then not become effective. It would ofcourse also be possible to retrofit devices already on hand with thehelp of add-on units. A possible principle of a switch-over is shown inFIG. 26. The outputs of ws 0, 1, 2, . . . and sw 0, 1, 2, . . . arerespectively connected to two gates. These gates only become active as afunction of a potential which is respectively applied to one of the twogates via the reversing switch U. If coding of the group 3 is intended,the switch is in the position 3b, if the new coding is to be used, theswitch U is in the position 3n. If, for example, white 1 is marked andthe switch U is at 3b, the gate G4 is connected to the potential onetime via ws1and another via U/3b, so that the coding of the group 3becomes active. If, however, the switch is at U/3n, then there is apotential on both inputs of the gate G3, so that it can then becomeactive. As can be seen from FIGS. 23 to 25, the coding ws 1 can beassigned to arbitrary numbers. If, for example, the coding sw0 is notneeded, no gate is connected to it for the new mode of operation. Thisis only one example of switching.

A further reduction of the transmission time can be attained in thatduring coding of only white or black lines the code word for white orblack is provided only once, and subsequently the code word for thenumber of the respective lines, such as the code word for 1728 white,and following that the number of the white lines, for example 83. Withtypewritten pages there is normally a white distance of 4 mm between thelines. This would result in thirty-two lines with a resolution of 8.Since white lines occur very often, it would be possible, for example,to provide a short code word for 1728. It is of course advantageous ifthe written line has the same horizontal position as the inserted page.The collection of the number of white lines can take place for examplein such a way, that a counter is controlled by means of the white linecode word until a code word for black sw appears. The output which isthen marked at the counter is evaluated in the central control, codedand either stored or immediately sent via modem to the transmissionpath. In FIG. 27, the coding white line ws1728 is switched to thecounter Z, so that the counter is advanced with every coding by oneoutput. The counter itself is connected with its outputs to the centralcontrol unit ZSt. The black code words sw are connected via a monostableswitch, which is delayed in activation. Such a connection is alsoprovided directly to the central control ZSt. The counter level is nowimmediately determined, stored, if required, and coded. The counter isreturned into the initial position via sw, MS. Via the transmissionpath, the central control provides the receiver with the code word forwhite lines and subsequently the number of white lines via the coder,the modem and the switch-on unit. Upon receipt of the code word "whiteline" on the receiver side, the output corresponding to the number ofwhite lines is marked on a counting device. The recording unit is thencontrolled from the central control, with white lines an immediatecontinuous switching then takes place until the number of the storedspaces has been switched. A principle of the comparison between thestored number of white lines and the switched white number is shown inFIG. 28. As soon as white lines are marked, the counter Z2 is startedvia J. Thirty-two lines are marked in the example. Therefore aconnection has been made to a gate G1, to which the thirty-second outputof the counting member is connected via another input. As soon as thecounting member Z2 has reached the output thirty-two, the continuedswitching of the counting member is interrupted via stop by means of thepotential now appearing at the output of G1. The counting member Z3 isalso controlled via the recording unit with the switching of the whitelines via ZJ. When the output thirty-two is reached at the countingmember 22, the gate G2 becomes active, by means of this furtherswitching of the white lines is stopped.

During transmission of gray, the principle of using the same code wordsfor white and black does result in considerable time savings. However,they are not yet satisfactory. Below further possibilities of graycoding and transmission are revealed. Up to now and as shown in FIG. 29,it was the custom for coding the gray shadings also with only white andblack pixels to change the halftones into more or less dense patterns ofblack and white pixels. In this case the scanning unit evaluates theanalogous voltage values. The step 0 is assigned to the white pixel inthis case and to the black one the step 16 or, with a better resolution,the step 64. The steps are then changed into corresponding patterns,some of which are shown in FIGS. 29a-d. In this manner it is thenpossible to process the information further as a black or white pixel.From this it becomes clear that there are always short run lengths to betransmitted, so that transmission becomes very time-consuming. In thefollowing exemplary embodiments ways are shown how it is possible toachieve a shortening of the transmission time of the gray imagetransmission. A plurality of pixel voltages are shown in FIG. 31. 1 isblack and corresponds to 16 steps, 2=14, 3=8 steps, etc. White and blackoccur very seldom in a gray image, so that the steps located at whiteand, if necessary also those at black, are separately coded andtransmitted.--The transformation of the pixel steps in accordance withthe Dither process takes place only in the receiver.--Thus, first thefirst four steps are coded and transmitted line-by-line, as shown inFIG. 32, and then the remaining steps. The code used in group 3, forexample, will be used as the code. In FIG. 4, for example, there are novalues under 4 up to the pixel voltage 6. Thus, the value 4 would beassigned sw2=11, for example. As already described in connection with afurther characteristic of the invention, since 4 appears six times in arow, a coded number 6 will be provided after the code word for 4, forexample, if 4 occurs 96 times in a row, the coded number for 96following the code word for 4. It is possible in this way to transmit alarge amount of line information already. The same can be provided forthe steps 13, 14, 15 and 16. With gray images the main information willlie between the steps 5 and 13. It is of course possible in the same wayto transmit the difference of the steps in relation to the end step 16.It is easily possible to provide individual microprocessors for thetraffic between large companies or offices, which then calculate therespectively most time-saving transmission coding. Intermediate storageis always practical.

A further possibility of shortened transmission is to code the 16 steps,as with teletype operations, and to transmit them in this way. With abinary code, two to the fourth power code elements would be required. Itwould be of course possible to use the run length coding of the group 3as well. With sequentially appearing similar code words it would againbe possible to send the number of the sequential code words to thereceiver by means of a number. With this method it is possible to reducethe transmission time once again. This effect can be increased if aredundancy is purposely introduced into the code, for example byproviding a 5-digit binary code for the 16 steps. An example of this isshown in FIG. 30. 32 combinations are possible with these five digits,the same as in the teletype code No. 2, indicated by I-32 in FIG. 30.The five code elements are then transmitted in two lines, once with twoand another time with three respectively combined. In FIG. 30, the codeelements of columns 4 and 5 are provided for the one line, and the codeelements of lines 1, 2 and 3 for the other. In the example it isintended to use the code words which are started with black in column 5for the coding of the 16 steps. Thus, only the code elements black/blackand black/white are always used. It is then possible to provide theshortest code of the group 3 for them, namely 2sw and 3sw. Sequences ofthe one or the other coding very often appear in these two codings, sothat the effect of coding and transmitting the number of sequences oftenoccurs. The 3-digit code words of columns 1, 2 and 3 appear respectivelythree times, so that eight code words must be provided for the threecolumns. If the columns 3, 4 and 5 and 1, 2 are respectively combined inone line, then only four code words are required per line.

In FIG. 31 it is also possible to provide a two-line transmission and touse the 8 as initial line. In this case the values 0, 0, 0, 0, 0, 0, 2would occur for the pixels 1, 2, . . . 7 against 0, and the values 8, 6,0, 0, 6, 4, 0 against 16.

It is also possible, respectively analogous to FIG. 17, to transmit thevalues 8 to 0 and 8-16, or two pixels simultaneously. In this case R-Ywould be assigned to the pixels 1, 3, 5, . . . and B-Y to the pixels 2,4, . . . It would also be possible to transmit 2×QAM simultaneously, ifone is associated with the upper sideband and the other with the lowersideband of a carrier and respectively filter out one of the two bymeans of filters and combine the bands not filtered out. Such aprinciple has been disclosed in U.S. Pat. No. 2,907,830, for example. Itis of course possible to apply this principle also to the transmissionof color TV signals.

If a large amount of written text with large left margins must betransmitted, it is possible to divide these into a fixed edge, indicatedby LR in FIG. 33, and a differing letter-start edge LB. It is then onlynecessary to transmit the fixed edge once, and the edge LB is thentransmitted every time. Such an edge coding can be made manually or canbe automatically determined by means of a microprocessor.

I claim:
 1. Data-reducing coding method for transmitting informationfrom a transmitter to a receiver, comprising the steps of:sampling theanalog information (PAM) with predetermined sampling frequency;quantifying the sampling values; storing the quantified sampling valuesin memory; determining an optimal reference level for a sequence ofquantified sampling values, for sections of a line, of plural lines, ofa block, of plural blocks; coding the reference level and the quantifiedsampling values on the basis of the determined reference level; codingsubsequently occurring equal values in the sequence of quantifiedsampling values, in the sections of a line, of plural lines, of a block,of plural blocks such that the coded number of subsequently occurringequal values is provided in combination with said equal value;transmitting the coded reference level, the coded values and apredetermined code to the receiver; and evaluating the transmittedvalues on the basis of the transmitted reference level and of thetransmitted predetermined code at the receiver.
 2. Coding method inaccordance with claim 1, characterized in that numbers are codeddigit-by-digit (e.g. 28 by code word 2 and by code word 8).
 3. Codingmethod in accordance with claim 1, characterized in that the codingmethod is used with telefax, digital speech transmission and/ortelevision.
 4. Coding method in accordance with claim 1, characterizedin that for telefax the gray tones are transformed at the receiver inaccordance with the Dither process.
 5. Coding method in accordance withclaim 1, characterized in that the reference level is determined eitherby a maximum level value or by a minimum level value for the sequence ofquantified sampling values, for the sections of a line, of plural lines,of a block, of plural blocks.
 6. Coding method in accordance with claim1, characterized in that color separations of base colors are coded andtransmitted for colored image patterns for telefax and television. 7.Coding method in accordance with claim 1, characterized in that adigital amplitude/phase code with reference phase relation and withleading or lagging phase relations is provided as a code fortransmitting the quantified sampling values on the basis of thedetermined reference level.